Maintenance of a substrate processing apparatus for manufacturing a semiconductor device, such as a large-scale integrated circuit (IC), is periodically performed to maintain the cleanliness therein. Conventionally, a gas cleaning technique of introducing a cleaning gas into a reaction chamber has been used to remove a film deposited on an element of the reaction chamber.
However, since the conventional gas cleaning technique is aimed at removing a film adsorbed into a reaction chamber, a non-reactive gas may be adsorbed onto or by-products may remain in piping of an exhaust system even after gas cleaning is completed. When a non-reactive gas is adsorbed into or by-products remain in the piping of the exhaust system, a vacuum exhaust apparatus may be unexpectedly stopped or an apparatus maintenance process may be difficult to perform.